High rate li/moo3 organic electrolyte cell

ABSTRACT

A FURTHER IMPROVEMENT IN THE PERFORMANCE OF LI/MOO3 IN TERMS OF THE RATE CAPABILITY AND THE ENERGY DENSITY, BY THE ADDITION OF SO2 IN THE ELECTROLYTE.

Aug. 13, 1974 A. N. DEY 3,829,330

men RATE m uoo ORGANIC ELECTROLYTE cm Original Filed Aug. 27, 1969 2 Sheets-Sheet 1 LITHIUM CATHODE TAB INV NTOR.

A N.Dey BY ATTORNEY Aug. 13, 1974 A. N. DEY 3,829,330

HIGH RATE Li/lleO ORGANIC ELECTROLYTE CELL Original Filed Aug. 27, 1969 2 Sheets-Sheet 2 FIG.3

c 0.50 AMP.

(Li/M003 CELL WITH 50:)

QZSAMP CELL VOLTAGE 30 HOURS United States Patent 3,829,330 HIGH RATE Li/MoO ELECTROLYTE Arabinda Narayan Dey, Needham, Mass, assignor to P. R. Mallory & Co. Inc., Indianapolis, Ind.

Continuation of application Ser. No. 853,312, Aug. 27,

1969, now Patent No. 3,808,052. This application Aug. 11, 1971, Ser. No. 170,710

Int. Cl. H01m 35/02 US. Cl. 136-6 LN 9 Claims ABSTRACT or THE DISCLOSURE A further improvement in the performance of Li/MoO in terms of the rate capability and the energy density, by the addition of S0 in the electrolyte.

new and improved electrolyte for use in the lithium/ organic electrolyte cell systems, with the organic electrolyte battery having substantially improved performance in terms of its rate capability and energy density.

It is another object of the present invention to provide a new lithium/M00 organic electrolyte cell utilizing a co-depolar'izer for obtaining a simultaneous discharge with the M00 to thereby increase the cell capacity and the high energy density of the cell.

It is a further object of the present invention to provide a novel organic electrolyte and cathode combination comprising an organic solvent having S0 dissolved therein; a cathode the active material of which comprises M00 immersed in the organic electrolyte, and with the dissolved S0 acting as a co-depolarizer with the M00 It is a still further object of .the present invention to provide an organic electrolytelcell comprising a light metal anode such as lithium; a cathode the active material of which comprises M005 and which further contains an electrically conductive carbon particle material; and an organic electrolyte comprising an organic solvent having a conductive salt dissolved therein and having S0 dissolved therein, with the dissolved S0 acting as a codepolarizer with the Mo0 Q Other and furtherobjects of the present invention will be apparent from the following description here and after.

FIG. 1 is a drawing of the anode cathode subassembly wound into a cylindrical roll.

FIG. 2 is a cross-section of the top portion of an assembled cell structure of the present invention.

FIG. 3 is a voltage time curve for test cells with and without S0 in the electrolyte.

Generally speaking, the present invention provides a new battery system in which the problem of low rate capability in an organic electrolyte cell is substantially overcome. This substantial improvement is the direct result of the presence, in the battery, of a novel depolarizer and codepolarizer combination comprised of a cathode the active material of which comprises M00 being immersed in an organic electrolyte which comprises an organic solvent having SO and a salt dissolved therein. The dis- 3,829,330v Patented Aug. 13, 1974 solved S0 acts as a co-depolarizer with the M00 and undergoes simultaneous discharge therewith.

The Li/MoO organic electrolyte cell described in the application S.N. 853,312 exhibited high output voltage, high energy density and long shelf life.

It has been discovered that it is possible to achieve substantial improvements in the performance of the above cell in terms of the rate capability and the energy density, by the addition of S0 to the electrolyte. In this instance, S0 acts as a co-depolarizer with the M00 so that both the M00 and S0 are discharged simultaneously giving rise to the increased cell capacity and the high rate capability. v

The principle of co-depolarization of an insoluble cathode by a soluble co-depolarizer viz S0 that has been discovered here, is novel. The phenomenon relies on the juxtaposition of thermodynamic potentials of the insoluble depolarizer and the soluble co-depolarizer. For example, in this specific case of M00 the thermodynamic potentials of the Li/MoO cell and the Li/SO cell are quite similar and consequently, the discharge of the Li/MoO cell with S0 added to the electrolyte, results in the initial reduction of M00;, to M00 which is again oxidized by S0 to M00 by a chemical reaction such as, 2MoO +SO 2MoO +S thereby regenerating or recharging the insoluble depolarizer M00 In this instance, the phenomenon can be viewed upon as in situ chemical charging of the cathode or cathode pumping. This principle is distinctly different from that described by Meyers et al. (US. 3,423,242) where S0 was used for increasing the conductivity and the decomposition potential of the electrolyte. According to this invention, all insoluble depolarizers, as disclosed by Meyers et al., are not suitable for such cathode pumping. The suitability of a depolarizer for such actions disclosed here, will depend on the thermodynamic potentials of depolarizers. This distinction has not been made by Meyers et al.

The cell described here is also distinctly difierent from that disclosed by Maricle et al. (US. 3,567,515) where S0 was used as the sole soluble depolarizer. According to this invention, the capacities of both the insoluble depolarizer, viz M00 and the soluble depolarizer, viz S0 are realized due to an effective simultaneous discharge of both, thereby resulting in an improvement in the cell performance over those disclosed by Meyers et al. and Maricle et al.

The Li/MoO cell was constructed in a cylindrical configuration by winding a 1.75 x 13.25" strip of flexible M00 cathode, a 1.65" x 14" strip of lithium anode and two 2.0" x 14" strips of 0.0005 thick nonwoven polypropylene fabric separators into a cylindrical roll, as shown in FIG. 1. The roll was then packaged in a D size cylindrical steel can as shown in FIG. 2. The lithium anode tab (5) from the roll was spot welded to the metal ring support (2) which was in contact with the wall of the can and the cathode tab (6) from the roll was spot welded to the aluminum top (4). The aluminum top had a threaded hole (10) which was used as electrolyte fill .port. The top was crimp sealed using EPR or butyl rubber gasket (3). The cell was chilled in Dry Ice before adding chilled electrolyte consisting of a mixture of one part by volume of 1.75 (M) LiBr in a mixture of acetonitrile (AN) and propylene carbonate (10:3 volume ratio), saturated with S0 (approximately 7.5 (M) and one part by a volume of liquid S0 Approximately 20 cc. of the above electrolyte was added through the electrolyte fill port. The electrolyte fill port was sealed with a bolt (7) fitted with a butyl rubber gasket (8) and the cell top was covered with epoxy in order to prevent any mechanical loosening of the fill port bolt. The round head of the bolt protruded out of the epoxy layer (9) and served as a positive terminal of the cell. The cell can served as the negative terminal.

The M cathode was made by pasting a premixed dough type mixture of M00 carbon, asbestos fiber and colloidal Teflon onto the expanded aluminum current collector, curing it at elevated temperatures and then cutting it to proper size (1.75" x 13.25). The thickness of the cathode was approximately 0.040" and the weight of the mix was approximately 9 grams. The aluminum collector located at the one end of the cathode.

The lithium anode was made by pressing a 0.020" thick lithium ribbon onto the expanded stainless steel current collector. Nickel tabs were spot welded to one end of the anode.

Discs of separator material were used at the bottom and at the top of the electrode roll inside the can in order to provide electrical insulation.

The cells made in the above manner were discharged at 0.250 amp and 0.50 amp constant drain. The voltage time curves are shown in FIG. 3 curve B and C. The capacity recovered above the 2.0 volt cutoif, was 7 a.hr. at 0.25 amp, and 6 a.hr. at 0.50 amp.

The Li/MoO cell was also made in the similar manner except no S0 was added in the electrolyte, and it was discharged at 0.25 amp drain. The discharge curve is shown in FIG. 3 curve A. The capacity recovered up to the 2.0 volt cutoff was only 0.85, a.hr. compared to 7 a.hr. obtained in the cells which contained S0 in the electrolyte. Thus an eight fold improvement in the cell performance has been achieved.

The improvement of the rate capability of the Li/MoO cell, with the addition of S0 in the electrolyte is particularly impressive. For example, the capacity recovered at twice the current i.e. 0.5 amp was 6 a.hr.; which was approximately seven times greater than the capacity recovered at half the current (0.25 amp) with the Li/MoO cell without S0 The scope of the invention and the improvements referred to are applicable to all Li/MoO organic electrolyte cells with (a) Solvents such as tetrahydrofuran, propylene carbonate, dimethyl sulfite, N-nitrosodimethyl amine, gammabutyrolactone, N:N dimethyl formamide, dimethyl sulfoxide, dimethyl carbonate, methyl formate, butyl formate and acetonitrile and the mixtures thereof.

(b) And electrolyte salts such as lithium halides, perchlorate, hexafluorophosphate, tetrafluoroborate, hexa- 'fluoroarsenate and tetrachloroaluminate.

Although the present invention has been disclosed in connection with a few preferred embodiments thereof, variations and modifications may be resorted to by those skilled in the art without departing from the principles of the new invention. All of these variations and modifications are considered to be within the true spirit and scope of the present invention as disclosed in the foregoing description and defined by the appended claims.

What is claimed is:

1. An organic electrolyte cell comprising an anode; a cathode the active material of which comprises M00 and an organic electrolyte comprising an organic solvent having S0 dissolved therein, said dissolved S0 acting as a co-depolarizer with the M00 and said organic electrolyte having a conductive lithium salt dissolved therein.

. 2. The organic electrolyte cell of claim 1 "wherein the anode is a light metal such as lithium.

3. The organic electrolyte cell of claim 2 wherein the cathode further comprises an electrically conductive carbon particle material. 1

4. The organic electrolyte cell of claim 3-.Wherein' the organic solvent is selected from the group consisting of tetrahydrofuran, propylene carbonate, dimethyl sulfite, N-nitrosodimethyl amine, 'gamma-butyrolactone, N:N dimethyl formamide, dimethyl sulfoxide, dimethylca'rbonate, methyl formate, butyl formate, acetonitrile, and mixtures thereof. 1 I

5. The organic electrolyte cellof claim 41-wherein' the organic electrolyte further comprises a dissolved conductive lithium salt selected from the group consisting of halides, perchlorates, hexafluorophosphates, te'trafluoroborates, hexafluoroarsenates, and tetrachloroaluminates.

6. An organic electrolyte in combination with a cathode for use in an organic electrolyte cell comprising an organic solvent having S0 and a conductive lithium salt dissolved therein; a cathode the active material of which comprises M00 being immersed in said organic electrolyte; said dissolved S0 acting as a co-depolarizer with the M00 7. The organic electrolyte cathode combination of claim 6 wherein the cathode further comprises an electrically conductive carbon particle material. I

8. The organic electrolyte cathode combination of claim 7 wherein the organic solvent is'selected from the group consisting of tetrahydrofuran, propylene carbonate, dimethyl sulfite, N-nitrosodimethyl amine, gamma-butyrolactone, N:N dimethyl formamide, dimethyl sulfoxide, dimethyl carbonate, methyl formate, butyl formate, acetonitrile, and the mixtures thereof. V

9. The organic electrolyte cathode combination of claim 8 wherein the salt is a lithium salt selected from the group consisting of halides, perchlorates, hexafluorophosphates, tetrafluoroborates, hexafluoroarsenates, and tetrachloroaluminates.

References Cited STATES PATENTS WINSTON A. DOUGLAS, Primary Examiner 1 C. F. LEFEVOUR, Assistant Examiner U.S. c1. X.R. 136-20 1 

